1. Field of Invention
This invention relates to a Reception Antenna Arrangement for Satellite And/or Terrestrial Radio Signals on Motor Vehicles
2. Prior Art
Satellite radio signals in satellite radio systems such as in the satellite radio system known as the SDARS, are transmitted with circular polarization, as a rule. For reception regions with substantially free propagation, a directional diagram with an azimuthal round diagram with a gain of about 3dBi for angles of elevation greater than 20 or 30 degrees is required to receive these signals. Antennas of this type and the requirements that have to be satisfied by the directional diagram are described, for example in PATSIOKAS ET AL: Satellite; SAE 2001-01; ISSN 0148-7191,3/2001. The relatively high requirement with respect to the gain in the range of low elevation angles is conditioned by the low angles of incidence of the satellite radio waves that frequently occur because of the positions of the satellites.
To support the supply of satellite radio systems with satellite radio signals, such as with the SDARS system, additional terrestrial radio stations operating on a transmitting frequency that slightly deviates from the satellite radio frequency are provided. The terrestrially transmitted waves are vertically polarized. To receive these signals the object is to azimuthally aim for a round diagram of the receiving antenna with a heightened gain at low angles of incidence, and with the omission of high gain values in connection with steep radiation, i.e. for about the directional diagram of a vertical, linear antenna. A combination antenna of this type is also specified in the literature source cited above. Transmitting the same information content of additional terrestrial radio stations, which reaches the receiver with minor time offset, is provided particularly for populated regions. In the event of any discontinuance of the satellite radio connection caused by shadowing due to buildings, trees etc., the total receiving information is coordinated in the digital plane of the receiver and united to form the radio signal. To further support the transmission reliability for the radio signal, a second time-offset satellite signal is provided in connection with the SDARS systems with the same information content so as to secure an optimal reception result.
In urban areas, the wave directly incident from the satellite is frequently superposed by waves scattered on objects, so that a Rice distribution of the antenna reception signals occurs, and, if the direct sight connection to a satellite breaks off, even a Rayleigh distribution will frequently occur as well. Measurements have shown that the local signal fading, events caused thereby may lead to a substantial loss of information even at frequencies of around 2.3 GHz due to the depth of the signal fading and because of the low signal levels of the satellite radio signals in the receiver. Even though these effects are counteracted, for example in SDARS systems, with the help of the multiple supply with two satellite signals, and in urban regions with an additional terrestrial supply, a break-off or loss of the radio connection occurs only in isolated cases. Building this break-off up again takes up an annoying amount of time because of the required coordination and synchronization of the components of the information individually received in the receiver.